Turning to FIG. 1, a conventional system 100 can be seen. This system 100 generally comprises a motor controller 102, a power supply 104, an inverter 106, and a motor 108 (which is typically a PMSM, BLDC, or induction motor). In operation, the motor controller 102 provides generally continuous pulse width modulation (PWM) signals (i.e., 6 PWM signals if the motor 108 is a three-phase motor). These PWM signals are used to control the inverter 106, so that the inverter 106 can provide the commanded voltage to each phase of motor 108 from power supply 104.
The motor controller 102 provides control of motor 108 (through the application of the PWM signals) based on a field-oriented control (FOC) algorithm. For conventional FOC control, there are typically three control loops (one speed loop and two current loops) that are employed to provide adjustments. Typically, the observer 120 forms a portion of the speed loop and determines a feedback speed or feedback signal ω from the PWM signals (provided to the inverter 106) and from the motor 108. A difference between this feedback signal ω and a reference speed or reference signal ω* (which is determined by assert 110-1) is adjusted by the proportional-integral (PI) controller 112-1 to generate the reference torque current iq* for the quadrature axis or q-axis. Additionally, a field weakener 114 provides the reference field current id* for the direct axis d-axis (in normal operation, id*=0 for PMSM and BLDC motors and id* is constant for induction motors). The observer 120 also determined the rotor position or angle and provides the angle signal θ to the Park converter 118 and PWM controller 116. The current loops generally include the Park converter 118, which determines currents id and iq from phase current measurements and the angle signal θ. These currents id and iq are then compared to or subtracted from the reference current id* and iq* by adders 110-2 and 110-3, respectively, to generate errors ΔId and ΔIq. These errors ΔId and ΔIq can then be further adjusted by PI controllers 112-2 and 112-3, and the commanded voltages Vd and Vq, along with the angle signal θ (which form a voltage command vector {right arrow over (V)}), can be used to generate the PWM signals, and generation of the PWM signals is usually accomplished by an inverse Park transformation (performed by an inverse Park converter within PWM controller 116) and a space vector PWM generator (within the PWM controller 116) so as to generate three phase voltages.
Turning to FIGS. 2A and 2B, an example of the construction of a voltage command vector {right arrow over (V)} from the voltage signals Vq* and Vd* and the commanded angle signal θ* for a three-phase motor can be seen. Typically, though, voltage signal Vd* much less than Vq*. The example voltage vector {right arrow over (V)} is located in sector I (having an angle σ). From this voltage vector {right arrow over (V)}, there are two resultant projections T1 and T2 that correspond to intervals over which the vectors V1 and V2 are applied over the associated PWM period (shown in FIG. 2B). These intervals T1 and T2 and vectors V1 and V2 are typically generated by a space vector PWM (SVPWM) in PWM controller 116. For this example, one-half of each of intervals T1 and T2 (over which vectors V1 and V2 are applied, respectively) are located are at each end of the PWM period with the remainder of the PWM period being the zero vector V7 or V0 (where no current is flowing in a direct current link or DC-link single-shunt). For low speed and some operations, intervals T1 and T2 (either one or both) are very small (as shown in FIGS. 3A and 3B), so a fast (and costly) analog-to-digital converter (ADC), which performed the data conversion for Park converter 118, is generally employed.
Thus, there is a need for a lower cost motor controller.
Some examples of conventional systems are: U.S. Pat. No. 5,886,498; U.S. Pat. No. 7,202,629; U.S. Pat. No. 7,208,908; U.S. Pat. No. 7,339,344; U.S. Pat. No. 7,646,164; U.S. Pat. No. 7,808,201; U.S. Patent Pre-Grant Publ. No. 2010/0201298; U.S. Patent Pre-Grant Publ. No. 2011/0012544; Ancuti et al., “Sensorless V/f control of high-speed surface permanent magnet synchronous motor drives with two novel stabilizing loops for fast dynamics and robustness,” IET Electr. Power Appl., Vol. 4, Iss. 3, 2010, pp. 149-157; Itoh et al., “A comparison between V/f control and position-sensorless vector control for the permanent magnet synchronous motor,” Proc. of the Power Conversion Conf., 2002. PCC Osaka 2002, pg. 1310-1315; and Perera et al., “A Sensorless, Stable V=f Control Method for Permanent-Magnet Synchronous Motor Drives”, IEEE Trans. on Ind. Appl., Vol. 39, No. 3, May/June 2003.